This invention relates to a process for modifying the surface of polypropylene or polyethylene to improve surface adhesion properties, especially to a process for bonding a maleic acid-polypropylene or polyethylene graft copolymer to polypropylene or polyethylene.
Polypropylene and polyethylene are common, relatively inexpensive, plastic used in fibers, films, and other articles. They has many useful properties, but are difficult to blend with or bond to other polymers. As a rule, these polymers do not readily adhere to other polymers. CELGARD.RTM. polypropylene fiber (made by Hoechst Celanese Corp., Charlotte, N.C.) is an example of a commercial polypropylene fiber.
Block and graft copolymers are often used as compatibilizers. See, e.g., U.S. Pat. Nos. 3,483,273, 3,860,442, 4,081,424, 4,107,130, and 4,110,303, the disclosures of which are herein incorporated by reference.
Polyolefins having functional monomers grafted thereon are known in the art. Acrylic acid grafted polypropylene, for instance, is produced by BP Chemicals, which sells this polymer as part of its POLYBOND.RTM. product line. This product is used as a reactive compatibilizer for preparing polypropylene-polyester and polypropylene-polyamide blends. However, acrylic acid grafting causes polyolefins to degrade significantly, reducing the intrinsic viscosity, molecular weight, and other properties of the polymer; furthermore, the active surface area of the product copolymer is relatively low. Graft copolymers of this type are disclosed in U.S. Pat. Nos. 4,455,273 and 4,584,347, the disclosures of which are herein incorporated by reference.
Hoechst Celanese Corporation makes HOSTAPRIME.RTM. HC 5, a maleic anhydride-grafted low molecular weight polypropylene coupling agent. Maleic anhydride grafted polyolefins are also available from BP Chemicals under the POLYBOND.RTM. tradename. These products are used in polymer blends to improve the compatibility of blended polymers, e.g. in polypropylene-polyamide blends.
Pending U.S. patent application No. 622,563, filed Dec. 5, 1990, now U.S. Pat. No. 5,173,541 describes a graft copolymer comprising a polyolefin backbone or main chain, preferably polypropylene, having muconic acid groups pendant therefrom. The acid groups are bonded to the backbone of the polyolefin by free radical addition across a muconic acid double bond.